Wireless local area network antenna system and method of use therefore

ABSTRACT

An embodiment of the present invention provides an apparatus, comprising a plurality of sub-arrays and at least one beamformer driving the plurality of sub-arrays, the at least one beamformer employing at least one phase shifter.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a divisional of U.S. patent application Ser. No.10/850,991, entitled, WIRELESS LOCAL AREA NETWORK ANTENNA SYSTEM ANDMETHOD OF USE THEREFORE”, to Shamsaifar et al. which claimed the benefitof priority under 35 U.S.C Section 119 from U.S. Provisional ApplicationSer. No. 60/472,599, filed May 22, 2003, entitled, “Wireless Local AreaNetwork Antenna System”, by Shamsaifar et al., assigned to ParatekMicrowave, Inc.

BACKGROUND OF THE INVENTION

The present invention generally relates to electronically beam steeringphased array antennas, tunable phase shifter, and tunable dielectriccapacitors.

Multipath delay causes the information symbols represented in an 802.11signal to overlap, which confuses the receiver. This is often referredto as intersymbol Interference (ISI). Because the shape of the signalconveys the information being transmitted, the receiver will makemistakes when demodulating the signal's information. If the delays aregreat enough, bit errors in the packet will occur. The receiver won't beable to distinguish the symbols and interpret the corresponding bitscorrectly.

When multipath strikes in this way, the receiving station will detectthe errors through 802.11's error checking process. The CRC (cyclicredundancy check) checksum will not compute correctly, indicating thatthere are errors in the packet. In response to bit errors, the receivingstation will not send an ACK to the source. The source will theneventually retransmit the signal after regaining access to the medium.

Because of retransmissions, users will encounter lower throughput whenmultipath is significant. The reduction in throughput depends on theenvironment. As examples, 802.11 signals in homes and offices mayencounter 50 nanoseconds multipath delay while a manufacturing plantcould be as high as 300 nanoseconds.

Thus, there is a strong need in the RF industry and more particularly inthe wireless local area network industry for wireless devices, networks,methods and systems which may overcome multipath and other RFtransmission shortcomings to improve performance in a wireless localarea network.

SUMMARY OF THE INVENTION

The present invention provides an apparatus, comprising an activereceive aperture and a multiple scanning beamformer receiving signalsfrom said active receive aperture via at least one low noise amplifier(LNA) stage and at least one beamformer, the at least one beamformer mayemploy at least one phase shifter. The phase shifters may comprise avoltage tunable dielectric material and the voltage tunable dielectricmaterial may be Parascan® dielectric material.

BRIEF DESCRIPTION OF THE DRAWINGS

The subject matter regarded as the invention is particularly pointed outand distinctly claimed in the concluding portion of the specification.The invention, however, both as to organization and method of operation,together with objects, features, and advantages thereof, may best beunderstood by reference to the following detailed description when readwith the accompanying drawings in which:

FIG. 1 is an illustration of one embodiment of the antenna system of thepresent invention;

FIG. 2 is an illustration of another embodiment of the antenna system ofthe present invention;

FIG. 3 is an illustration of yet another embodiment of the antennasystem of the present invention.

It will be appreciated that for simplicity and clarity of illustration,elements illustrated in the figures have not necessarily been drawn toscale. For example, the dimensions of some of the elements areexaggerated relative to other elements for clarity. Further, whereconsidered appropriate, reference numerals have been repeated among thefigures to indicate corresponding or analogous elements.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Although tunable materials in general can be utilized and areanticipated by the present invention, one tunable material that isdescribed in an embodiment of the present invention is Parascan®.Parascan® is a trademarked tunable dielectric material developed byParatek Microwave, Inc., the assignee of the present invention. Tunabledielectric materials are the materials whose permittivity (more commonlycalled dielectric constant) can be varied by varying the strength of anelectric field to which the materials are subjected or immersed.Examples of such materials can be found in U.S. Pat. Nos. 5,312,790,5,427,988, 5,486,491, 5,693,429 and 6,514,895. These materials show lowdielectric loss and high tunability. Tunability is defined as thefractional change in the dielectric constant with applied voltage. Thepatents above are incorporated into the present application by referencein their entirety. Parascan® voltage tunable dielectric materials areembodied within software controlled tunable filters, diplexers, matchingnetworks and phased-array antennas, tunable notch filters, null-steerantennas, smart antennas, tunable phase shifters, voltage controlledoscillators (VCO's) and voltage tunable dielectric capacitors. The termsParascan® voltage tunable capacitors, Parascan® variable capacitors,Parascan® tunable dielectric capacitors and Parascan® varactors have thesame meaning and are interchangeable herein.

Existing antenna configurations for wireless networks may utilize anantenna configuration that is based on multiple fixed beams. Forexample, there may be 13 independent beams that support threesimultaneous packets on three different channels. The 10 other unusedbeams when not in “listening” or “scanning” mode may be used solely todetect new user access requests. Since the beams are narrow, multipathproblems may be reduced to some extent, but since the sidelobes or theslope of the main beam can still detect multipath signals, it is noteliminated completely. If the number of beams is reduced, for example,and not by way of limitation, from 13 to 4, the multipath negativeeffects may be reduced. However, with a reduced number of beams, thenumber of users that can be covered efficiently may also be reduced.Another concern for the existing system is that the 3.8 dB crossover orscalloping loss typical in multiple adjacent fixed beams may causecapacity and throughput reduction. Yet another concern for the existingsystems is that if the users decide to move around inside the coveragerange, they will face even more degraded quality of service.

The present invention provides an improved wireless local area networkby improving antenna system throughput. This may be accomplished bymitigating multipath; improving signal to interference ratio; andreducing the system hardware cost by eliminating unused beams.Furthermore, by using scanning beams, the present invention may providemobility and may track mobile users and may even provide location-basedservices. This improved wireless local area network antenna system mayuse electronically scanning wireless local area network (WLAN) phasedarray antennas that may use tunable phase shifters which may incorporatea tunable material. Further, this tunable material in an embodiment ofthe present invention may use Parascan® tunable material. Although thepresent invention is not limited in this respect.

Turning now to the figures, FIG. 1 illustrates an antenna system, showngenerally as 100, with a passive aperture 120 driven by a Butler Matrixbeamformer 110 which may be used for transmit only. A transmit switchmatrix 105 with transmit ports 115 may provide the input to Butlermatrix 110.

An active receive aperture 175 may be used in the present invention andin one embodiment may be capable of handling 4 or more independentlysteerable beams. In one embodiment, the receive aperture may have 16columns of elements to provide this functionality. Although, the presentinvention is not limited to any particular number of rows or columns.Also, it is understood that the number of steerable beams and whether ornot they are independently steerable or not is merely illustrative ofone embodiment and it is understood that a large number of steerablebeams are within the scope of the present invention.

The active beamformer 130 for receiving may include low noise amplifiers(LNA) stages 135, 140, 145 and 150, and beamformers 155, 160, 165 and170 which in one embodiment of the present invention may employ phaseshifters. One type of phase shifter that may be utilized in the presentinvention, although it is understood that the present invention is notlimited in this respect, are phase shifters based on Parascan® tunablematerials. Receiving output from the LNAs is a multiple scanning beamformer 130 with receive ports 125.

In one embodiment of the present invention, one beam may be dedicated tofinding new users and user requests, and to monitor interference.Although it is understood that one beam or more than one beam canaccomplish this in alternate embodiments of the present invention. Oncethe scanning beam has identified the users (in one embodiment asdescribed herein, the users may be up to three simultaneous packets onthree difference channels), the other 3 or more beams may be directed topoint to each of the users at the maximum gain. Thus, the system of thepresent invention covers essentially the same number of users with fewerindependent beams than the current state of the art systems. In thisembodiment, 4 scanning beams may replace 13 fixed beams. This may reducethe size and complexity of the antenna hardware and produce betterperformance by reducing multipath effects. Since most of the WLAN usersare fixed users, the present invention allows for a methodology toprofile the interference environment. The methodology could also beself-learning and adaptive by adding a feedback loop, thereby improvingthe interference reduction over time and adapting to changes in theinterference profile. The use of continuously steerable beams alsoenables the tracking of mobile users. Further, phase shifters can alsobe added in the transmit path which could provide additional systemimprovement.

Another problem with the current state of the art approaches, which mayconsist of several adjacent fixed beams, is the existence of crossoveror scalloping loss of typically 3.8 dB. As depicted in FIG. 2, showngenerally as 200, the present invention overcomes this shortcoming byadding phase shifters 235 between the Butler matrix 230 and theradiating columns 240. In this way, the present invention provides forthe potential to control the phase shifters and thereby enable theability change the directions of the beams pointed to the users by up tohalf the beam spacing and to reduce the crossover loss down to 0.5 dBfrom 3.8 dB. As the phase shifters may have an additional loss of about0.5 dB, the benefit may be up to 2.8 dB. Since more phase shift may beneeded at the edges of the array, the associated more loss towards theedges of the array may also improve the sidelobe levels to some extent,which will further improve the multipath problem. Transmit switch matrix205 with transmit ports 215 as well as receive switch 210 with receiveports 220 feed into diplexers 225 (in one embodiment 13 diplexers areused). Diplexers 225 provide input to and receive output from butlermatrix 230.

The present invention also advances the state of the art by improvingthe signal to interference ratio as well. This may be achieved by nullthe steering capability of the multi beam steerable antenna of thepresent invention. Since all of the beams may be steered simultaneously,the signal to interference ratio and the cross-over loss may be improvedby optimizing the beamsteering such that the interferers will be asclose as possible to pattern nulls, and the users as close as possibleto pattern maxima.

Turning now to FIG. 3, another embodiment of the present invention isshown generally at 300. This embodiment may be particularly useful,although not limited in this respect, to situations where only moderateantenna gain is needed; and thus enables an eloquent system capable ofhandling up to 3 simultaneous beams. Three cylindrical sub-arrays 334,336 and 338, each producing a 22.5 deg beamwidth in elevation and 45 degin azimuth can be stacked up to create a single cylindrical form factorof not more than about 18inches high and 2.8 inches in diameter. It isunderstood that the beamwidth, elevation, azimuth and stack size andnumber articulated herein, and any number form factors with varyingheight and width, are merely one embodiment of the present invention anda wide array of elevations, azimuths and stack sizes as well as anynumber of cylinder form factors with varying heights and widths areintended to be within the scope of the present invention.

Each sub-array 334, 336 and 338 in one embodiment is capable of scanninga 45 deg wide beam in azimuth through 360 degrees. Although the presentinvention is not limited in this respect. In one embodiment of thepresent invention, a 12 dBi gain antenna system may be provided.Beamformers (3 in one preferred embodiment of the present invention) 330with RF I/O ports (3 in one preferred embodiment of the presentinvention) drive sub-array 334, 336 and 338.

While the present invention has been described in terms of what are atpresent believed to be its preferred embodiments, those skilled in theart will recognize that various modifications to the discloseembodiments can be made without departing from the scope of theinvention as defined by the following claims.

1. An apparatus, comprising: a plurality of radiating columns; atransmit switch matrix transmitting through said plurality of radiatingcolumns via at least one diplexer associated with a Butler matrixfurther associated with at least one phase shifter; and a receive switchmatrix receiving information from said plurality of radiating columnsvia at least one diplexer associated with a Butler matrix furtherassociated with at least one phase shifter.
 2. The apparatus of claim 1,further comprising transmit ports associated with said transmit switchmatrix and receive ports associated with said receive switch matrix. 3.The apparatus of claim 1, wherein said phase shifters comprise a voltagetunable dielectric material.
 4. The apparatus of claim 3, wherein saidvoltage tunable dielectric material is Parascan® dielectric material. 5.An apparatus, comprising: a plurality of sub-arrays; and at least onebeamformer driving said plurality of sub-arrays, said at least onebeamformer employing at least one phase shifter.
 6. The apparatus ofclaim 5, wherein said phase shifters comprise a voltage tunabledielectric material.
 7. The apparatus of claim 6, wherein said voltagetunable dielectric material is Parascan® dielectric material.
 8. Theapparatus of claim 6, wherein said plurality of sub-arrays is 3subarrays, enabling scanning a 45 degree beam in azimuth through 360degrees and handling up to 3 simultaneous beams.
 9. The apparatus ofclaim 8, wherein said 3 subarrays each are capable of producing a 22.5degree beamwidth in elevation and 45 degrees in azimuth and may bestacked to create a single form factor.